Gallium arsenide growth in a pancake MOCVD reactor

We present a modeling study of the growth of gallium arsenide layers deposited onto a high-temperature susceptor in a pancake metalorganic chemical vapor deposition reactor. We analyzed the deposition process with a two-dimensional model that is axisymmetric about the vertical axis. The model includes detailed fluid flow, heat-and mass-transfer, and gas-phase and surface chemistry. The chemistry includes reactions to model the incorporation of carbon into the semiconductor as GaC. The mass transfer includes thermal diffusion for tri-, di- and mono-methyl gallium, as well as for three corresponding Ga-carbene species that are the precursors of GaC formation. The inclusion of a detailed reaction mechanism resulted in a very wide range of timescales, creating a challenging numerical problem. We found that the rate of gallium arsenide deposition and its uniformity over the susceptor depend strongly on the temperature of the susceptor, and are relatively insensitive to the rate of rotation of the susceptor up to 200 rpm, the maximum rotation-rate studied. Nonetheless, the dependence of the radial distribution of GaAs growth on the rate of susceptor rotation is notable in that it appears possible to determine an optimum rotation rate for this reactor. The flow state in the reactor is dominated by buoyancy up to a rotation rate of about 100 rpm. The buoyancy-driven recirculation above the susceptor could pose problems as an unwanted storage mechanism for reactants, which could hinder the ability to generate sharp interfaces between successive layers. (C) 1998 Published by Elsevier Science B.V. All rights reserved.